Current research on this grant is directed to the identification, activities and properties of inorganic pyrophosphatases in relation to cell proliferation. Our specific aims are: 1. To ascertain the nature and properties of the inorganic pyrophosphatases in a selected series of normal and neoplastic cell types; and to determine the existence of multiple forms and their relationships with other phosphatases. 2. To explore whether pyrophosphate can serve as a phosphate donor in various phosphate transfer reactions, as in various micro-organisms. 3. To explore the nature and extent of cytotoxic effects of inhibitors of pyrophosphatase, particularly with respect to DNA synthesis and breakdown. 4. To establish the extent to which inorganic pyrophosphatase activities from various cells overlap in substrate specificity with the alkaline phosphatase isozymes.